Vehicle-body structure of vehicle

ABSTRACT

A vehicle-body structure which prevent deformation of a floor tunnel caused by a side collision load transmitted from a cross member to the floor tunnel via a seat mounting bracket. A pair of left and right backbone frames extending in a vehicle front-rear direction are provided each of which faces a top and a side of a floor tunnel and is fixed to the floor tunnel. A tunnel reinforcement is provided that includes a front projection, an intermediate projection, and a rear projection abutting on an underside of the floor tunnel. The backbone frame includes multiple beads abutting on the floor tunnel. The tunnel reinforcement is fixed at the front projection, the intermediate projection, and the rear projection to the seat mounting bracket via the floor tunnel and is also fixed to the multiple beads of the backbone frame via the floor tunnel.

BACKGROUND Technical Field

The present disclosure relates to a vehicle-body structure of a vehiclethat can withstand a collision from a side of the vehicle.

Background Art

In general, if a B pillar (center pillar) of a vehicle such as anautomobile intrudes into a passenger compartment of the vehicle under aside collision load that acts on a side sill at a side of the vehicledue to another vehicle colliding with the side of the vehicle or theside of the vehicle colliding with an obstacle, an occupant will beinjured. Thus, a cross member extending in a vehicle width direction ofthe vehicle has been used to receive the side collision load acting onthe side sill and prevent the B pillar from intruding into the passengercompartment.

In vehicles such as front-engine rear-drive (FR) vehicles and four-wheeldrive (4WD) vehicles, a floor tunnel extending in a front-rear directionand having a huge cross-section is provided to dispose a propeller shaftthat transmits power from a drive source located frontward to drivewheels located rearward. It is important to prevent the side collisionload acting via the cross member from concentrating on the floor tunnelwith such a huge cross-section.

For example, Japanese Patent Laid-Open No. 2015-134520 discloses astructure in which a cross member abuts on an upper member extending inthe front-rear direction between a side sill and a floor tunnel and alsoabuts on a connecting member provided at a side wall portion of thefloor tunnel.

Japanese Patent Laid-Open No. 2019-014354 discloses a lower vehicle-bodystructure in which, in order to increase both of the rigidity of a sidecollision load transmission path and the rigidity of a seat mountingportion, a seat mounting bracket mounted to a cross member is joined viaa floor tunnel to a tunnel reinforcement provided at an underside of thefloor tunnel.

However, the vehicle-body structure disclosed in Japanese PatentLaid-Open No. 2019-014354 has the following problem. When the vehicleincludes a floor tunnel with a huge cross-section like theaforementioned FR vehicle, the tunnel reinforcement itself becomeslarge, and thus the side collision load, which is transmitted from thecross member to the tunnel reinforcement via the seat mounting bracketand the floor tunnel, cannot be received by the tunnel reinforcementalone. This renders the floor tunnel prone to deformation.

SUMMARY

The present disclosure has been made in view of the above conventionalproblem and aims to provide a vehicle-body structure of a vehicle thatcan prevent deformation of the floor tunnel caused by the side collisionload transmitted from the cross member to the floor tunnel via the seatmounting bracket.

Accordingly, the present disclosure is a vehicle-body structure of avehicle, the vehicle-body structure including a pair of left and rightside sills extending in a front-rear direction of a vehicle; floorpanels extending from vehicle-width-direction inner side ends of theside sills toward a vehicle-width-direction inner side; a floor tunnelconnecting vehicle-width-direction inner side ends of the floor panelsand having a shape protruding upward; a pair of left and right crossmembers connecting the side sills and the floor tunnel; a seat mountingbracket mounted to both ends in a vehicle width direction of the crossmember; a pair of left and right backbone frames facing a top and a sideof the floor tunnel and fixed to the floor tunnel, the pair of left andright backbone frames extending in a vehicle front-rear direction; and atunnel reinforcement having a front projection, an intermediateprojection, and a rear projection abutting on an underside of the floortunnel. The backbone frame includes a plurality of beads abutting on thefloor tunnel, and the tunnel reinforcement is fixed at the frontprojection, the intermediate projection, and the rear projection to theseat mounting bracket via the floor tunnel and is also fixed to theplurality of beads of the backbone frame via the floor tunnel.

Ridges of the front projection, the intermediate projection, and therear projection of the tunnel reinforcement and ridges of the beads ofthe backbone frame are in contact with each other.

The vehicle-body structure includes a first front abutting portion, afirst intermediate abutting portion, and a first rear abutting portionabutting on the plurality of beads of the backbone frame respectively atthe front projection, the intermediate projection, and the rearprojection, and includes a second front abutting portion, a secondintermediate abutting portion, and a second rear abutting portionabutting on the seat mounting bracket.

The vehicle-body structure includes a front recess and a rear recessprotruding in a direction away from the underside of the floor tunnelrespectively between the front projection and the intermediateprojection and between the intermediate projection and the rearprojection.

The tunnel reinforcement includes an extended portion rearward of therear abutting portion, and the extended portion includes, at a rear endthereof, a rear end projection fixed to an additional bead of thebackbone frame.

The vehicle-body structure further includes a rear end recess protrudingin a direction away from the underside of the floor tunnel between therear projection and the rear end projection.

According to the disclosure, the tunnel reinforcement is fixed at thefront projection, the intermediate projection, and the rear projectionto the seat mounting bracket via the floor tunnel and is also fixed tothe multiple beads of the backbone frame via the floor tunnel. Thisallows the side collision load input from the cross beam to the seatmounting bracket in the event of a side collision to be transmitted tothe multiple beads of the backbone frame via the front projection, theintermediate projection, and the rear projection of the tunnelreinforcement, and this restrains deformation of the tunnelreinforcement as well as the floor tunnel.

According to the disclosure, ridges of the front projection, theintermediate projection, and the rear projection of the tunnelreinforcement are in contact with ridges of the beads of the backboneframe. This allows the side collision load to be surely transmitted tothe multiple beads of the backbone frame via the front projection, theintermediate projection, and the rear projection of the tunnelreinforcement.

According to the disclosure, the vehicle-body structure includes a firstfront abutting portion, a first intermediate abutting portion, and afirst rear abutting portion abutting on the multiple beads of thebackbone frame respectively at the front projection, the intermediateprojection, and the rear projection, and includes a second frontabutting portion, a second intermediate abutting portion, and a secondrear abutting portion abutting on the seat mounting bracket. This allowsfor easy and reliable joining of the tunnel reinforcement and thebackbone frame and of the tunnel reinforcement and the seat mountingbracket via these abutting portions.

According to the disclosure, the vehicle-body structure includes a frontrecess and a rear recess protruding in a direction away from theunderside of the floor tunnel respectively between the front projectionand the intermediate projection and between the intermediate projectionand the rear projection. This increases the rigidity of the tunnelreinforcement with these continuous projections and recesses.

According to the disclosure, the tunnel reinforcement includes anextended portion rearward of the rear abutting portion, and the extendedportion includes, at a rear end thereof, a rear end projection fixed toan additional bead of the backbone frame. This increases the rigidity ofthe floor tunnel and surely restrains deformation of the floor tunneleven when the side collision load is input from the seat mountingbracket to a front portion of the tunnel reinforcement.

According to the disclosure, the vehicle-body structure includes a rearend recess protruding in a direction away from the underside of thefloor tunnel between the rear projection and the rear end projection.This increases the rigidity of the tunnel reinforcement with thesecontinuous projections and recess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a lower vehicle-body of an automobile having avehicle-body structure according to an embodiment of the presentdisclosure;

FIG. 2 is a perspective view of a first cross member and a second crossmember of the lower vehicle-body as viewed from a vehicle front sidetoward a vehicle rear side;

FIG. 3 is a sectional view of the first cross member in a vehicle widthdirection;

FIG. 4 is an enlarged exploded perspective view showing components ofthe first cross member;

FIG. 5A is a perspective view showing an example of a fragile portion ata portion where a first member of the first cross member is mounted to aside sill, FIG. 5B is a perspective view showing a modification of thefragile portion, and FIG. 5C is a perspective view showing anothermodification of the fragile portion;

FIGS. 6A-6C are plan views showing a procedure for mounting the firstcross member;

FIG. 7 is a sectional view of the second cross member in the vehiclewidth direction;

FIG. 8 is an enlarged perspective view of a joining portion of atunnel-side seat mounting bracket of the second cross member and a floortunnel;

FIG. 9 is an enlarged exploded perspective view showing how thetunnel-side seat mounting bracket of the second cross member isconnected to the floor tunnel, a tunnel reinforcement, and a backboneframe;

FIG. 10A is a sectional view along the line Xa-Xa in FIG. 9, and FIG.10B is a sectional view along the line Xb-Xb in FIG. 9.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described below withreference to the accompanying drawings. Throughout the drawings,reference characters Fr and Rr respectively refer to a front side (orfrontward) and a rear side (or rearward) of an automobile, and referencecharacters OUT and IN respectively refer to an outside (or outward) andan inside (or inward) of the automobile in the vehicle width direction.

<Overall Structure of Lower Vehicle-Body>

FIG. 1 shows a lower vehicle-body 1 of the automobile having avehicle-body structure of a vehicle according to an embodiment of thepresent disclosure. The lower vehicle-body 1 includes a pair of left andright side sills 2 extending in a vehicle front-rear direction, a floortunnel 3 disposed at a center in the vehicle width direction between thepair of left and right side sills 2 and extending in the vehiclefront-rear direction, and floor panels 4 extending fromvehicle-width-direction inner side ends of the pair of left and rightside sills 2 toward a vehicle-width-direction inner side up to the floortunnel 3.

A pair of left and right floor frames 5 each extending in the vehiclefront-rear direction between a corresponding one of the pair of left andright side sills 2 and the floor tunnel 3 are disposed in the lowervehicle-body 1 each as a reinforcement member. A first cross member 6and a second cross member 7 laid between each one of the pair of leftand right side sills 2 and the floor tunnel 3 are disposed in this ordertoward the vehicle rear side.

An oblique frame 8 extending obliquely rearward from each one of thepair of left and right side sills 2 to a corresponding one of the pairof left and right floor frames 5 is disposed frontward of the firstcross member 6. A third cross member 9 laid in the vehicle widthdirection between each one of the pair of left and right side sills 2and the floor tunnel 3 is disposed rearward of the second cross member7.

Meanwhile, the lower vehicle-body 1 includes, in its front portion, adash panel 10 a, a dash panel cowl 10 b, a pair of left and right frontside frames 11, a bumper reinforcement 12, a front cross member 13,apron members 14, a suspension housing 15, and the like. The lowervehicle-body 1 includes, in its rear portion, a pair of left and rightrear side frames 16 extending from respective rear ends of the pair ofleft and right side sills 2 to the vehicle rear side, a rear floor panel17 extending in the vehicle width direction between the pair of left andright rear side frames 16, and a rear cross member 18. Detaileddescription of the oblique frame 8, the third cross member 9, and thefront and rear components of the lower vehicle-body 1 has been omittedas they do not relate directly to the present disclosure.

<Side Sill>

As shown in FIG. 3, each of the pair of left and right side sills 2 iscomposed of a side sill inner panel 20 with a cross-section of ahat-shaped profile opening toward the vehicle-width-direction outer sideand a side sill outer panel 21 with a cross-section of a hat-shapedprofile opening toward the vehicle-width-direction inner side.

The side sill inner panel 20 includes a top face 22, a side face 23extending downward from a vehicle-width-direction inner side end of thetop face 22, a bottom face 24 extending from a lower end of the sideface 23 toward the vehicle-width-direction outer side, an upper ridgeportion 25 between the top face 22 and the side face 23, and a lowerridge portion 26 between the bottom face 24 and the side face 23. Areinforcement plate 27 is fixed inside the side sill inner panel 20 atmultiple positions in the vehicle front-rear direction, particularlypositions overlapping the first cross member 6 and the second crossmember 7 in the vehicle front-rear direction.

The side sill outer panel 21 has a shape similar to that of the sidesill inner panel 20 and facing the side sill inner panel 20. The sidesill inner panel 20 and the side sill outer panel 21 are joined so as toform a substantially rectangular closed cross-section in the vehiclewidth direction. Lower portions of a hinge pillar supporting a frontdoor and a center pillar supporting a rear door are joined to the sidesill 2, though not shown in the figures.

<Floor Tunnel>

As shown in FIG. 1, the floor tunnel 3 extends in the vehicle front-reardirection from the dash panel 10 a to the third cross member 9. As shownin FIG. 2, the floor tunnel 3 has a hat-shaped profile opening downwardand protruding upward in its cross-section in the vehicle widthdirection. Specifically, as shown in FIG. 3, the floor tunnel 3 iscomposed of a flange portion 30 joined to the floor panel 4, a wallrising portion 31 rising upward from the flange portion 30, a raisedportion 32 extending from the wall rising portion 31 toward thevehicle-width-direction inner side and positioned one step higher thanthe flange portion 30, an inclined wall portion 33 obliquely rising fromthe raised portion 32 toward the center in the vehicle width direction,and a top plate portion 34.

A pair of left and right backbone frames 35 is mounted on a top side ofthe floor tunnel 3. Each of the pair of left and right backbone frames35 has an inverted L-shaped cross-section in the vehicle width directionso as to form a closed cross-section with the top plate portion 34 andthe inclined wall portion 33 of the floor tunnel 3 which the backboneframe 35 faces. An upper flange portion 36 and a lower flange portion 37are provided at respective ends in the vehicle width direction of thebackbone frame 35. The upper flange portion 36 and the lower flangeportion 37 are respectively joined to the top plate portion 34 and theinclined wall portion 33 of the floor tunnel 3. In particular, as shownin FIG. 9, the lower flange portion 37 of the backbone frame 35 isformed with multiple beads 38 (linearly extending recesses orprojections formed by pressing a material) extending in the vehiclewidth direction at its portions joined to the floor tunnel 3 atpositions thereof overlapping the second cross member 7 in the vehiclefront-rear direction. The multiple beads 38 are joined to a tunnelreinforcement 100 (described later) through the floor tunnel 3.

A mount member 39 a for supporting a rear portion of a transmission (notshown) is mounted to an underside of the raised portion 32 on both sidesof the floor tunnel 3 in the vehicle width direction, and this restrainsthe decrease in vehicle-body rigidity that would otherwise occur due tothe first cross members 6 on both sides being separated by the floortunnel 3.

<Floor Panel>

Returning to FIG. 3, the floor panel 4 extends from avehicle-width-direction inner side end of the side sill 2 toward thevehicle-width-direction inner side. In other words, avehicle-width-direction outer side end of the floor panel 4 is joined tothe side face 23 of the side sill inner panel 20, and avehicle-width-direction inner side end of the floor panel 4 is joined tothe flange portion 30 on both sides of the floor tunnel 3 in the vehiclewidth direction. Also, the floor panel 4 extends in the vehiclefront-rear direction from the dash panel 10 a to the third cross member9 in FIG. 1.

The floor panel 4 includes a step portion 40 provided at an approximatecenter between the side sill 2 and the floor tunnel 3 and extending inthe vehicle front-rear direction, a first floor panel 41 on thevehicle-width-direction inner side of the step portion 40, and a secondfloor panel 42 on the vehicle-width-direction outer side of the stepportion 40. The step portion 40 is provided with a floor frame 5described later. The second floor panel 42 is formed at a position lowerthan the first floor panel 41. In other words, the second floor panel 42located between a floor upper frame of the floor frame 43 and the sidesill is formed at a position lower than the first floor panel locatedbetween the floor upper frame and the floor tunnel 3. This allows arectifier (not shown) to be only provided below the first floor panel 41and eliminates the need for providing the rectifier below the secondfloor panel 42, helping reduce the area of the rectifier.

Each of the pair of left and right floor frames 5 is provided such thatthe step portion 40 of the floor panel 4 is interposed in the floorframe 5 in an up-down direction, and extends in the vehicle front-reardirection. The floor frame 5 is composed of a floor upper frame 50forming a closed cross-section jointly with a top side of the stepportion 40 of the floor panel 4, and a floor lower frame 51 forming aclosed cross-section jointly with an underside of the step portion 40 ofthe floor panel 4.

The floor upper frame 50 includes a frame top face 50 a facing the firstfloor panel 41, a frame side face 50 b extending from avehicle-width-direction inner side end of the frame top face 50 a to thefirst floor panel 41, and a frame side face 50 c extending from avehicle-width-direction outer side end of the frame top face 50 a to thesecond floor panel 42. The frame top face 50 a of the floor upper frame50 is provided at a position higher than a center position P between theupper ridge portion 25 and the lower ridge portion 26 of the side sill 2in the up-down direction. A lower end of the frame side face 50 b on thevehicle-width-direction inner side is joined to a top side of the firstfloor panel 41, and a lower end of the frame side face 50 c on thevehicle-width-direction outer side is joined to a top side of the secondfloor panel 42.

The floor lower frame 51 includes a frame bottom face 51 a facing thefirst floor panel 41, a frame side face 51 b extending from avehicle-width-direction inner side end of the frame bottom face 51 a tothe first floor panel 41, and a frame side face 51 c extending from avehicle-width-direction outer side end of the frame bottom face 51 a tothe second floor panel 42. The frame bottom face 51 a of the floor lowerframe 51 is provided at substantially the same position as the secondfloor panel 42. An upper end of the frame side face 51 b on thevehicle-width-direction inner side is joined to an underside of thefirst floor panel 41, and an upper end of the frame side face 51 c onthe vehicle-width-direction outer side is joined to an underside of thesecond floor panel 42.

<First Cross Member>

The first cross member 6 is composed of a first member 61 on a sidesill-side and a second member 62 on a floor tunnel-side. The firstmember 61 is mounted with a sill-side seat mounting bracket 60, and thesecond member 62 is mounted with a tunnel-side seat mounting bracket 63.

The first member 61 extends from the side sill 2 to the frame top face50 a of the floor upper frame 50. As shown in FIG. 4, the first member61 has a hat-shaped cross-section in the vehicle front-rear directionand includes a top face 64 facing the floor panel 4 and a front face 65and a rear face 66 extending from respective ends in the vehiclefront-rear direction of the top face 64 to the floor panel 4. The frontface 65 and the rear face 66 respectively includes a front lower portion65A and a rear lower portion 66A at positions lower than the first floorpanel 41.

Flanges 65 a, 66 a are provided to respective vehicle-width-directionouter side ends of the front face 65 and the rear face 66 of the firstmember 61, and the flanges 65 a, 66 a are joined to the side face 23 ofthe side sill 2. Flanges 65 b, 66 b are provided to respective lowerends of the front face 65 and the rear face 66 of the first member 61,and the flanges 65 b, 66 b are joined to the second floor panel 42.Flanges 65 c, 66 c, 65 d, 66 d are provided to vehicle-width-directioninner side ends of the front face 65 and the rear face 66 of the firstmember 61, and the flanges 65 c, 66 c are joined to the frame side face50 c of the floor upper frame 50 and the flanges 65 d, 66 d are joinedto the frame top face 50 a of the floor upper frame 50.

The top face 64 of the first member 61 includes, at itsvehicle-width-direction outer side end, a fragile portion 67 formed of acutout. The fragile portion 67 functions to transmit a side collisionload to the top face 64 of the first cross member 6 in the event of aside collision by cutting a part of the vehicle-width-direction outerside end of the top face 64 of the first member 61 as shown in FIG. 5Aand thereby allowing the vehicle-width-direction outer side end of thetop face 64 to be preferentially crushed under the side collision load.Besides the cutout, the fragile portion 67 may be a bead or a holeextending in the vehicle front-rear direction as shown in FIGS. 5B and5C; in short, the fragile portion 67 is only required to weaken therigidity in the vehicle width direction of the vehicle-width-directionouter side end of the top face.

A recessed bead 68 extending in the vehicle width direction is formed ineach of the front face 65 and the rear face 66 of the first member 61.Preferably, the beads 68 are provided above the second floor panel 42and below the aforementioned center position P between the upper ridgeportion 25 and the lower ridge portion 26 in the up-down direction ofthe side sill 2. The beads 68 increase the rigidity of the front face 65and the rear face 66 of the first member 61 against the side collisionload.

The second member 62 extends from a vehicle-width-direction inner sideend of the first member 61 to the floor tunnel 3. As shown in FIG. 3,the second member 62 has a hat-shaped cross-section in the vehiclefront-rear direction and includes a top face 69 facing the floor panel 4and a front face 70 and a rear face 71 extending from respective ends inthe vehicle front-rear direction of the top face 69 to the floor panel4.

A vehicle-width-direction outer side end of the top face 69 of thesecond member 62 is positioned below a vehicle-width-direction innerside end of the top face 64 of the first member 61 and, as shown in FIG.3, is overlapped with and joined to the vehicle-width-direction innerside end of the top face 64 of the first member 61 to form ahigh-strength portion 72 that has a larger plate thickness than thefront lower portion 65A and the rear lower portion 66A of the firstmember 61 and the front face 70 and the rear face 71 of the secondmember 62 and is given a high strength. Flanges 70 a, 71 a are providedto respective lower ends of the front face 70 and the rear face 71 ofthe second member 62, and the flanges 70 a, 71 a are joined to thesecond floor panel 42. The vehicle-width-direction outer side end of thetop face 69 of the second member 62 extends to a joined portion of thefirst member 61 and the sill-side seat mounting bracket 60, and thisgives the high-strength portion 72 a higher strength than ahigh-strength portion 86 (described later) between the second member 62and the tunnel-side seat mounting bracket 63.

A recessed bead 73 extending in the vehicle width direction is formed inthe top face 69 of the second member 62. The bead 73 is provided so asto overlap beads 78, 80 (described later) of the sill-side seat mountingbracket 60 in the vehicle front-rear direction.

The sill-side seat mounting bracket 60 is a fixing member for fixing aseat rail of the vehicle and is also a reinforcement member forreinforcing a sill-side end of the top face 64 of the first member 61 ofthe first cross member 6. The sill-side seat mounting bracket 60includes a top face 74 facing the top face 64 of the first member 61 anda front face 75 and a rear face 76 extending from respective ends in thevehicle front-rear direction of the top face 74 to the floor panel 4.

A seat rail mounting portion 77 protruding upward is formed at a centerin the vehicle width direction of the top face 74 of the sill-side seatmounting bracket 60. A recessed bead 78 extending in the vehicle widthdirection is formed at an end of the top face 74 on the outside of theseat rail mounting portion 77 of the sill-side seat mounting bracket 60.A protruding piece 79 protruding to the vehicle-width-direction outerside is formed at a vehicle-width-direction outer side end of the topface 74 of the sill-side seat mounting bracket 60, and the protrudingpiece 79 abuts on and is joined to the top face 22 of the side sill 2.An upward projecting bead 80 extending in the vehicle width direction isformed at an inner end of the top face 74 of the sill-side seat mountingbracket 60, and on both sides of the bead 80, the sill-side seatmounting bracket 60 abuts on and is joined to the top face 64 of thefirst member 61.

Multiple projecting beads 81 extending in the up-down direction areformed in each of the front face 75 and the rear face 76 of thesill-side seat mounting bracket 60, and on both sides of each bead 81,the front face 75 and the rear face 76 abut on and are joined to thefront face 65 and the rear face 66, respectively, of the first member61. Flanges 75 a, 76 a are formed on respective vehicle-width-directionouter side ends of the front face 75 and the rear face 76 of thesill-side seat mounting bracket 60, and the flanges 75 a, 76 a abut onand are joined to the side face 23 of the side sill 2.

The tunnel-side seat mounting bracket 63 is a fixing member for fixingthe seat rail of the vehicle. The tunnel-side seat mounting bracket 63extends from a vehicle-width-direction inner side end of the floor panel4 to the inclined wall portion 33 of the floor tunnel 3. Avehicle-width-direction outer side half of the tunnel-side seat mountingbracket 63 has a hat-shaped cross-section in the vehicle front-reardirection formed by a top face 82, a front face 83, and a rear face 84.A seat rail mounting portion 85 protruding upward is formed on a topside of a vehicle-width-direction inner side half of the tunnel-sideseat mounting bracket 63.

A vehicle-width-direction outer side end of the tunnel-side seatmounting bracket 63 is positioned below a vehicle-width-direction innerside end of the top face 69 of the second member 62 and is overlappedwith and joined to the vehicle-width-direction inner side end of the topface 69 of the second member 62 to form, as shown in FIG. 3, ahigh-strength portion 86 that has a larger plate thickness than thefront lower portion 65A and the rear lower portion 66A of the firstmember 61 and the front face 70 and the rear face 71 of the secondmember 62 and is given a high strength.

A flange 82 a is provided to a vehicle-width-direction inner side end ofthe tunnel-side seat mounting bracket 63, and the flange 82 a abuts onand is joined to the inclined wall portion 33 of the floor tunnel 3.

Flanges 82 b, 82 c are provided to each end in the vehicle front-reardirection of the vehicle-width-direction inner side half of thetunnel-side seat mounting bracket 63, and the flanges 82 b, 82 c abut onand are joined to the inclined wall portion 33 and the raised portion32, respectively, of the floor tunnel 3. Flanges 83 a, 84 a are providedto the front face 83 and the rear face 84, respectively, of thevehicle-width-direction outer side half of the tunnel-side seat mountingbracket 63, and the flanges 83 a, 84 a are joined to avehicle-width-direction inner side end of the first floor panel 41.

In assembling the first cross member 6, as shown in FIGS. 6A-6C, thetunnel-side seat mounting bracket 63 is first mounted to the floortunnel 3, and then the second member 62 is mounted so as to overlap avehicle-width-direction outer side end of the tunnel-side seat mountingbracket 63 (FIG. 6A). Then, a vehicle-width-direction inner side end ofthe first member 61 is overlapped with and mounted to avehicle-width-direction outer side end of the second member 62, and avehicle-width-direction outer side end of the first member 61 is mountedto the side sill 2 (FIG. 6B). Finally, the sill-side seat mountingbracket 60 is overlapped with and mounted to the first member 61, and avehicle-width-direction outer side end of the sill-side seat mountingbracket 60 is mounted to the side sill 2. (FIG. 6C). Two adjacentmembers or all members may be sub-assembled in advance.

<Second Cross Member>

Similarly to the first cross member 6, the second cross member 7 iscomposed of the first member 61 on the side sill-side and the secondmember 62 on the floor tunnel-side as shown in FIG. 7, and the firstmember 61 is mounted with the sill-side seat mounting bracket 60 and thesecond member 62 is mounted with the tunnel-side seat mounting bracket63.

The second cross member 7 has a similar structure to that of the firstcross member except that the second cross member 7 is positionedgenerally lower than the first cross member 6, the tunnel-side seatmounting bracket 63 is composed of a lower bracket 87 and an upperbracket 88, and a tunnel reinforcement 100 is provided inside the floortunnel 3 to which the tunnel-side seat mounting bracket 63 is mounted.Accordingly, description of equivalent parts has been omitted and onlydifferences will be described below.

Because the second cross member 7 is positioned generally lower than thefirst cross member 6, a flange 74 a protruding upward is provided to avehicle-width-direction outer side end of a top face of the sill-sideseat mounting bracket 60, and the flange 74 a abuts on and is joined tothe side face 23 of the side sill 2.

The tunnel-side seat mounting bracket 63 of the second cross member 7 iscomposed of the lower bracket 87 and the upper bracket 88.

The lower bracket 87 extends from the raised portion 32 of the floortunnel 3 to the vehicle-width-direction inner side end of the floorpanel 4. As shown in FIG. 8, a vehicle-width-direction outer side halfof the lower bracket 87 has a hat-shaped cross-section in the vehiclefront-rear direction formed by a top face 89, a front face 90, and arear face 91.

Via the raised portion 32 of the floor tunnel 3, the lower bracket 87 isbolted to both ends of a tunnel member 39 b that connects both ends inthe vehicle width direction of the floor tunnel 3, and this restrainsthe decrease in vehicle-body rigidity that would otherwise occur due tothe second cross members 7 on both sides being separated by the floortunnel 3.

A vehicle-width-direction outer side end of the lower bracket 87 ispositioned below a vehicle-width-direction inner side end of the topface 69 of the second member 62 and is overlapped with and joined to thevehicle-width-direction inner side end of the top face 69 of the secondmember 62 to form a high-strength portion 92 that has a larger platethickness than the front lower portion 65A and the rear lower portion66A of the first member 61 and the front face 70 and the rear face 71 ofthe second member 62 and is given a high strength.

Flanges 90 a, 91 a are formed at respective ends in the vehiclefront-rear direction of the front face 90 and the rear face 91 in thevehicle-width-direction outer side half of the lower bracket 87, and theflanges 90 a, 91 a abut on and are joined to the vehicle-width-directioninner side end of the floor panel 4. An inner end and front-reardirection ends in the vehicle-width-direction inner side half of thelower bracket 87 abut on and are joined to the raised portion 32 of thefloor tunnel 3.

The upper bracket 88 is disposed above the lower bracket 87. The upperbracket 88 is formed on its top side with a seat rail mounting portion93 protruding upward. A flange 88 a is provided to avehicle-width-direction outer side end of the upper bracket 88, and theflange 88 a abuts on and is joined to the top face 89 of the lowerbracket 87.

Flanges 88 b, 88 c, 88 d are provided to a vehicle-width-direction innerside end of the upper bracket 88, and these flanges 88 b, 88 c, 88 dabut on the inclined wall portion 33 of the floor tunnel 3 and arejoined to the tunnel reinforcement 100 (described later) via theinclined wall portion 33. Also, flanges 88 e, 88 f are provided torespective ends in the vehicle front-rear direction of the upper bracket88, and these flanges 88 e, 88 f abut on and are joined to the raisedportion 32 of the floor tunnel 3.

<Tunnel Reinforcement>

A tunnel reinforcement 100 is mounted to an underside of the floortunnel 3 to which the tunnel-side seat mounting bracket 63 of the secondcross member 7 is joined. The tunnel reinforcement 100 is substantiallysaddle-shaped with its cross-section in the vehicle width directionbeing in the form of an inverted U-shape opening downward.

As shown in FIGS. 10A and 10B, the tunnel reinforcement 100 includes afront projection 101, a front recess 102, a rear projection 103, a rearrecess 104, and a rear end projection 105 disposed in this order in thevehicle front-rear direction, and these are provided so as to extend ina circumferential direction. The rear projection 103 is formed, at itseach end in the vehicle width direction, a wide portion 106 that iswider than an intermediate portion of the rear projection 103. The frontrecess 102 includes, on its each side in the vehicle width direction, anintermediate projection 107 that is provided so as to extend in theup-down direction along the front projection 101 and the rear projection103. A first front recess 102 a and a second front recess 102 b areprovided to respective ends in the vehicle front-rear direction of theintermediate projection 107. When viewed from inside the tunnelreinforcement 100, the front projection 101, the first front recess 102a, the intermediate projection 107, the second front recess 102 b, andthe rear projection 103 form a substantially W-shaped cross-section inthe vehicle front-rear direction. Also, the rear projection 103, therear recess 104, and the rear end projection 105 form a substantiallyU-shaped cross-section in the vehicle front-rear direction.

The tunnel reinforcement 100 is joined to the underside of the floortunnel 3 and, as explained below, also joined to the backbone frame 35and the tunnel-side seat mounting bracket 63 via the floor tunnel 3.

That is, as shown in FIG. 10A, the front projection 101, theintermediate projection 107, the rear projection 103, and the rear endprojection 105 are respectively provided with a first front abuttingportion 101 a, a first intermediate abutting portion 107 a, a first rearabutting portion 103 a, and a first rear end abutting portion 105 a thatabut on and are welded to the respective beads 38 of the backbone frame35 via the floor tunnel 3.

Also, as shown in FIG. 10B, the intermediate projection 107 and the rearprojection 103 are respectively provided with a second intermediateabutting portion 107 b and a second rear abutting portion 103 b thatabut on and are welded to the flange 88 b of the tunnel-side seatmounting bracket 63 via the floor tunnel 3. Also, the front projection101 and the wide portion 106 of the rear projection 103 are respectivelyprovided with a second front abutting portion 101 b and a third rearabutting portion 106 a that respectively abut on and are welded to theflanges 88 c, 88 d of the tunnel-side seat mounting bracket 63 via thefloor tunnel 3.

The tunnel reinforcement 100 is provided with an extended portion 108rearward of the tunnel-side seat mounting bracket 63, and accordinglythe length of the tunnel reinforcement 100 in the vehicle front-reardirection is longer than that of the tunnel-side seat mounting bracket63 of the second cross member 7.

<Functions of Cross Members in the Event of Side Collision>

Below a description will be given of functions of the first cross member6 and the second cross member 7 of the above-configured lowervehicle-body 1 according to the present embodiment in the event of aside collision.

In the lower vehicle-body 1 of the present embodiment, the first crossmember 6 and the second cross member 7 extending in the vehicle widthdirection receive a side collision load F that acts on the side sill 2as shown in FIG. 1 when another vehicle collides with a side of thevehicle or when the side of the vehicle collides with an obstacle. Thisprevents a pillar (not shown) from intruding into a passengercompartment.

That is, as shown in FIG. 3, in the first cross member 6 in the lowervehicle-body 1 of the present embodiment, the top face 64 of the firstmember 61 is joined to the side sill 2 via the sill-side seat mountingbracket 60, the vehicle-width-direction inner side end of the top face64 of the first member 61 is joined to the vehicle-width-direction outerside end of the top face 69 of the second member 62, and thevehicle-width-direction inner side end of the top face 64 of the secondmember 62 is joined to a vehicle-width-direction outer side end of thetop face 82 of the tunnel-side seat mounting bracket 63, and thetunnel-side seat mounting bracket 63 is joined to the raised portion 32and the inclined wall portion 33 of the floor tunnel 3. Thus, the topfaces 64, 69, 74, and 82 of the first cross member 6 are joined to theside sill 2 and the floor tunnel 3 (the part A in FIG. 3).

Also, in the first cross member 6, the vehicle-width-direction outerside ends of the front face 65 and the rear face 66 of the first member61 are joined to the side sill 2, and the vehicle-width-direction innerside ends of the front face 65 and the rear face 66 of the first member61 are joined to the frame top face 50 a of the floor upper frame 50 ata position higher than the center position P of the side sill 2 in theup-down direction (the part B in FIG. 3).

Thus, the first cross member 6 can counteract a side collision load inthe event of a side collision with its first bracing effect provided bythe part A in FIG. 7 of the top faces 64, 69, 74, and 82 of the firstcross member between the side sill 2 and the floor tunnel 3 and with itssecond bracing effect provided by the part B in FIG. 7 of the front face65 and the rear face 66 of the first member 61 between the side sill 2and the frame top face 50 a of the floor upper frame 50, resisting theinwardly falling motion of the side sill 2 toward thevehicle-width-direction inner side as shown by the arrow M in FIG. 3.The same applies to the second cross member 7. Thus, even though thevehicle has a lowered floor including the second floor panel 42 lowerthan the first floor panel 41, the first cross member 6 and the secondcross member 7 can effectively distribute and transfer the sidecollision load F in the vehicle width direction from the side sill 2 tothe floor upper frame 50 and the floor tunnel 3.

Further, the bead 68 extending in the vehicle width direction isprovided in each of the front face 65 and the rear face 66 of the firstmember 61 of the first cross member between the side sill 2 and theframe side face 50 b. This prevents out-of-plane deformation (buckling)of the front face 65 and the rear face 66 and allows the side collisionload F to be effectively supported by the bracing between the side sill2 and the floor upper frame 50 in the event of a side collision, helpingavoid stress concentration on the floor tunnel 3 that may occur when theside collision load F is mainly supported by any bracing between theside sill 2 and the floor tunnel 3.

Additionally, the top faces 64, 69, 74, and 82 of the first cross member6 connect the raised portion 32 of the floor tunnel 3 and the side sill2, and the front face 65 and the rear face 66 of the first member 61connect the wall rising portion 31 of the floor tunnel 3 and the sidesill 2. This allows the side collision load F to be received between theside sill 2 and each of the wall rising portion 31 and the raisedportion 32 of the floor tunnel 3, helping avoid stress concentration onthe inclined wall portion 33 and the top plate portion 34, whichconstitute a main body of the floor tunnel 3.

<Functions of High-Strength Portions of Cross Member>

In the lower vehicle-body 1 of the present embodiment, the high-strengthportions 72, 86 having a larger thickness than the front lower portion65A and the rear lower portion 66A of the first member 61 and given ahigh strength are provided to the first cross member 6 and the secondcross member 7 at the overlapped portion of the sill-side seat mountingbracket 60 and the top face 64 of the first member 61, at the overlappedportion of the top face 64 of the first member 61 and the top face 69 ofthe second member 62, and at the overlapped portion of the top face 69of the second member 62 and the tunnel-side seat mounting bracket 63.This allows the side collision load F, which is input to the first crossmember 6 and the second cross member 7 so as to cause the side sill 2 tofall inward to the inside of the vehicle cabin in the event of a sidecollision, to be surely transmitted in the vehicle width direction viathe high-strength portions 72, 86. This can restrain deformation of thefront face 65 and the rear face 66 of the first member 61 facing thelowered second floor panel 42.

Since the high-strength portions 72, 86 are portions made by overlappingmultiple members including the first member 61, the second member 62,the sill-side seat mounting bracket 60 and the tunnel-side seat mountingbracket 63, the high-strength portions can be configured with a simpleconfiguration.

The sill-side seat mounting bracket 60 and the tunnel-side seat mountingbracket 63 are respectively mounted to the first member 61 and thesecond member 62 having the high-strength portions 72, 86, and thisrestrains deformation of the sill-side seat mounting bracket 60 and thetunnel-side seat mounting bracket 63 and reduces impact on an occupantsitting in the seat in the event of a side collision.

The sill-side seat mounting bracket 60, the first member 61, the secondmember 62, and the tunnel-side seat mounting bracket 63 are fixed toeach other such that one closer to the side sill 2 lies on top ofanother adjacent one closer to the floor tunnel 3. Accordingly, when theside collision load F causing inward falling deformation of the sidesill 2 is input to the first cross member 6 and the second cross member7, compressive force in the surface direction acts on the overlappedportion of each member, which can restrain peeling of the overlappedportion.

As shown in FIG. 2, the bead 73 on the top side of the second member 62is provided so as to overlap the beads 78, 80 of the sill-side seatmounting bracket 60 in the vehicle front-rear direction. This allows theside collision load F on the side sill 2 to be transmitted to thevehicle-width-direction inner side via the beads 78, 80 of the sill-sideseat mounting bracket 60 and the bead 73 of the second member 62.

<Functions of Fragile Portion in Cross Beam>

In the lower vehicle-body 1 of the present embodiment, the fragileportion 67 formed of a cutout extending in the vehicle front-reardirection is provided to a side-sill side end of the first member 61 ata position overlapping the sill-side seat mounting bracket 60 in each ofthe first cross member 6 and the second cross member 7.

In the event of a side collision, due to the side collision load F beingapplied to the side sill, a moment M acts on the side sill 2 so as tocause it to fall inward. Under this bending moment M, first, a proximalend of the protruding piece 79 of the sill-side seat mounting bracket 60joined to the top face 22 of the side sill 2 experiences out-of-planedeformation. Because the seat mounting bracket 60 on thevehicle-width-direction inner side of the protruding piece 79 has highrigidity by virtue of its hat-shaped cross-section, the side collisionis transmitted to the fragile portion 67 at the vehicle-width-directionouter side end of the top face 64 of the first member 61.

Thus, the fragile portion 67 of the first member 61 crushes and therebyabsorbs energy of the side collision, restraining buckling deformationof the first cross member 6 and the second cross member 7 from occurringin their portions where such deformation is not intended to occur.Further, guiding the side collision load F preferentially in thedirection in which the fragile portion 67 crushes allows to effectivelydistribute and transfer the side collision load F in the vehicle widthdirection.

Also, the sill-side seat mounting bracket 60 as the reinforcement memberis provided to the side sill-side end of the top face 64 of the firstmember 61 of each of the first cross member 6 and the second crossmember 7. Thus, the sill-side seat mounting bracket 60 as thereinforcement member can receive a region including the crushed fragileportion 67 and thereby allows the side collision load F after crushingthe fragile portion 67 to be transmitted in the vehicle width directionvia the sill-side seat mounting bracket 60 as the reinforcement memberas well as the first member 61 and the second member 62.

The fragile portion 67 is selected from a cutout, a bead, and a hole.Hence, the fragile portion 67 can be formed by simple processing andalso its deformation behavior in the event of a side collision can becontrolled.

The reinforcement member is the sill-side seat mounting bracket 60, andthe fragile portion 67 is positioned on the vehicle-width-directionouter side of the seat rail mounting portion 77 of the sill-side seatmounting bracket 60. Hence, even when the fragile portion 67 is crushedand deformed in the event of a side collision, it does not reach theseat rail mounting portion 77 of the sill-side seat mounting bracket 60,and thus impact on an occupant sitting on the seat can be reduced.

The fragile portion 67 is provided only on the top face 64 at the sidesill-side end of the first member 61. Hence, ridge portions between thetop face 64 and the front face 65 and between the top face 64 and therear face 66 remain uncrushed in the event of a side collision, allowingthe side collision load F to be transmitted in the vehicle widthdirection.

<Functions of Tunnel Reinforcement>

In the lower vehicle-body 1 of the present embodiment, as shown in FIG.9, the tunnel reinforcement 100 is fixed at its second front abuttingportion 101 b, second intermediate abutting portion 107 b, second rearabutting portion 103 b, and third rear abutting portion 106 a to thetunnel-side seat mounting bracket 63 via the floor tunnel 3. Also, thetunnel reinforcement 100 is fixed at its first front abutting portion101 a, first intermediate abutting portion 107 a, and first rearabutting portion 103 a to the multiple beads 38 of the backbone frame 35via the floor tunnel 3. Thus, the side collision load F input from thesecond cross member 7 to the tunnel-side seat mounting bracket 63 in theevent of a side collision is transmitted to the tunnel reinforcement 100via the second front abutting portion 101 b, the second intermediateabutting portion 107 b, the second rear abutting portion 103 b, and thethird rear abutting portion 106 a of the tunnel reinforcement 100 andfurther can be transmitted to the multiple beads 38 of the backboneframe 35 via the first front abutting portion 101 a, the firstintermediate abutting portion 107 a, and the first rear abutting portion103 a of the tunnel reinforcement 100. This restrains deformation of thetunnel reinforcement 100 as well as the floor tunnel 3.

Additionally, ridges of the first front abutting portion 101 a, thefirst intermediate abutting portion 107 a, and the first rear abuttingportion 103 a of the tunnel reinforcement 100 and ridges of the beads 38of the backbone frame 35 are in contact with each other. This allows theside collision load F to be surely transmitted to the multiple beads 38of the backbone frame 35 via the first front abutting portion 101 a, thefirst intermediate abutting portion 107 a, and the first rear abuttingportion 103 a of the tunnel reinforcement 100.

The tunnel reinforcement 100 includes, respectively in the frontprojection 101, the intermediate projection 107, and the rear projection103, the first front abutting portion 101 a, the first intermediateabutting portion 107 a, and the first rear abutting portion 103 a thatabut on the respective multiple beads 38 of the backbone frame 35, andincludes the second front abutting portion 102 a, the secondintermediate abutting portion 107 b, the second rear abutting portion103 b, and the third rear abutting portion 106 a that abut on the seatmounting bracket 63. This allows for easy and reliable joining of thetunnel reinforcement 100 and the backbone frame 35 and of the tunnelreinforcement 100 and the seat mounting bracket 63 via these abuttingportions.

The tunnel reinforcement 100 includes, respectively between the frontprojection 101 and the intermediate projection 107 and between theintermediate projection 107 and the rear projection 103, the frontrecess 102 a and the rear recess 102 b protruding in a direction awayfrom the underside of the floor tunnel 3. The tunnel reinforcement 100further includes the rear end recess 104 protruding in the directionaway from the underside of the floor tunnel 3 between the rearprojection 103 and the rear end projection 105. These continuousprojections and recesses can increase the rigidity of the tunnelreinforcement 100.

The tunnel reinforcement 100 includes the extended portion 108 rearwardof the rear abutting portion 103, and the extended portion 108 includes,at its rear end, a rear end projection 105 fixed to the additional bead38 of the backbone frame 35. This tunnel reinforcement 100 elongated inthe vehicle front-rear direction by virtue of its extended portion 108increases the rigidity of the floor tunnel 3, which as a result allowsto surely restrain deformation of the floor tunnel 3 even when the sidecollision load F is input from the seat mounting bracket 63 to the frontportion of the tunnel reinforcement 100.

The present disclosure is not limited to the above embodiment and may bemodified in various ways without departing from the scope of the presentdisclosure.

For example, although the tunnel-side seat mounting bracket 63 of thesecond cross member 7 is composed of the lower bracket 87 and the upperbracket 88, it may be composed of a single component similarly to thetunnel-side seat mounting bracket 63 of the first cross member 6.Conversely, the tunnel-side seat mounting bracket 63 of the first crossmember 6 may be composed of the lower bracket 87 and the upper bracket88 similarly to the tunnel-side seat mounting bracket 63 of the secondcross member 7.

What is claimed is:
 1. A vehicle-body structure of a vehicle, thevehicle-body structure comprising: a pair of left and right side sillsextending in a front-rear direction of a vehicle; floor panels extendingfrom vehicle-width-direction inner side ends of the side sills toward avehicle-width-direction inner side; a floor tunnel connectingvehicle-width-direction inner side ends of the floor panels and having ashape protruding upward; a pair of left and right cross membersconnecting the side sills and the floor tunnel; a seat mounting bracketmounted to both ends in a vehicle width direction of the cross member; apair of left and right backbone frames facing a top and a side of thefloor tunnel and fixed to the floor tunnel, the pair of left and rightbackbone frames extending in a vehicle front-rear direction; and atunnel reinforcement having a front projection, an intermediateprojection, and a rear projection abutting on an underside of the floortunnel, wherein each of the backbone frames includes a plurality ofbeads abutting on the floor tunnel, and the tunnel reinforcement isfixed at the front projection, the intermediate projection, and the rearprojection to the seat mounting bracket via the floor tunnel and is alsofixed to the plurality of beads of the backbone frames via the floortunnel.
 2. The vehicle-body structure of a vehicle according to claim 1,wherein ridges of the front projection, the intermediate projection, andthe rear projection of the tunnel reinforcement and ridges of the beadsof the backbone frames are in contact with each other.
 3. Thevehicle-body structure of a vehicle according to claim 2, furthercomprising: a first front abutting portion, a first intermediateabutting portion, and a first rear abutting portion abutting on theplurality of beads of the backbone frames respectively at the frontprojection, the intermediate projection, and the rear projection; and asecond front abutting portion, a second intermediate abutting portion,and a second rear abutting portion abutting on the seat mountingbracket.
 4. The vehicle-body structure of a vehicle according to claim3, further comprising: a front recess and a rear recess protruding in adirection away from the underside of the floor tunnel respectivelybetween the front projection and the intermediate projection and betweenthe intermediate projection and the rear projection.
 5. The vehicle-bodystructure of a vehicle according to claim 4, wherein the tunnelreinforcement includes an extended portion rearward of the rear abuttingportion, and the extended portion includes, at a rear end thereof, arear end projection fixed to an additional bead of the backbone frames.6. The vehicle-body structure of a vehicle according to claim 5, furthercomprising: a rear end recess protruding in a direction away from theunderside of the floor tunnel between the rear projection and the rearend projection.
 7. The vehicle-body structure of a vehicle according toclaim 1, further comprising: a first front abutting portion, a firstintermediate abutting portion, and a first rear abutting portionabutting on the plurality of beads of the backbone frames respectivelyat the front projection, the intermediate projection, and the rearprojection; and a second front abutting portion, a second intermediateabutting portion, and a second rear abutting portion abutting on theseat mounting bracket.
 8. The vehicle-body structure of a vehicleaccording to claim 1, further comprising: a front recess and a rearrecess protruding in a direction away from the underside of the floortunnel respectively between the front projection and the intermediateprojection and between the intermediate projection and the rearprojection.
 9. The vehicle-body structure of a vehicle according toclaim 1, wherein the tunnel reinforcement includes an extended portionrearward of the rear abutting portion, and the extended portionincludes, at a rear end thereof, a rear end projection fixed to anadditional bead of the backbone frames.
 10. The vehicle-body structureof a vehicle according to claim 7, further comprising: a front recessand a rear recess protruding in a direction away from the underside ofthe floor tunnel respectively between the front projection and theintermediate projection and between the intermediate projection and therear projection.
 11. The vehicle-body structure of a vehicle accordingto claim 7, wherein the tunnel reinforcement includes an extendedportion rearward of the rear abutting portion, and the extended portionincludes, at a rear end thereof, a rear end projection fixed to anadditional bead of the backbone frames.
 12. The vehicle-body structureof a vehicle according to claim 9, further comprising: a rear end recessprotruding in a direction away from the underside of the floor tunnelbetween the rear projection and the rear end projection.
 13. Thevehicle-body structure of a vehicle according to claim 11, furthercomprising: a rear end recess protruding in a direction away from theunderside of the floor tunnel between the rear projection and the rearend projection.